1. Field of the Invention
This invention relates to stock material for a container body of an insulating paper container having low melting point (m.p.) thermoplastic synthetic resin film laminated on the outer wall surface of said container body and expanded, the container and a process for making them.
2. Description of the Related Art
Japanese Patent Publication Gazette No. 1973-32283 describes the process comprising steps of laminating low m.p. thermoplastic synthetic resin film on at least one surface of moisture containing paper destined to become stock material for the container body and heating this film so that said film may be expanded to present an irregular surface under a pressure of water vapor discharged from said moisture containing paper constituting stock material. This literature describes also the technique such that the opposite surface of said paper is formed with a layer adapted to hold water vapor generated during the step of heating.
Japanese Patent Application Disclosure Gazette No. 1982-110439 describes, in regard to a paper container generally comprising the container body and the bottom wall, the process comprising steps of laminating low m.p. thermoplastic synthetic resin film on outer wall surface of said container body and heating this film so that said film may be expanded so as to present an irregular surface under a pressure of water vapor generated from moisture contained in the base paper. This literature describes also the technique such that a similar expandable thermoplastic synthetic resin film is laminated on the opposite surface of the base paper or this opposite surface is coated with aluminum foil so as to hold a pressure of water vapor generated during the step of heating.
Japanese Patent Application Disclosure Gazette No. 1993-42929 describes, in regard to the paper container generally comprising the container body and the bottom wall, the process comprising steps of doubly laminating low m.p. thermoplastic synthetic resin film and high m.p. thermoplastic synthetic resin film on outer wall surface of base paper of the container body and heating them so that only the low m.p. thermoplastic synthetic resin film forming the inner layer may be expanded and thereby the two-layered insulating paper container having the smooth and glossy outer layer. This literature described also the technique such that high m.p. thermoplastic synthetic resin film is laminated on the opposite surface of the base paper as a layer serving to hold a pressure of water vapor generated during heating treatment.
Japanese Patent Application Disclosure Gazette No. 1995-232774 describes, in regard to the paper container generally comprising the container body and the bottom wall, the process comprising steps of printing the base paper of the container body in a desired region on its outer wall surface with organic solvent containing ink, then laminating low m.p. thermoplastic synthetic resin film on said outer wall surface inclusive of the surface of said print, and heating this so that the printed region may be expanded more thickly than the remaining region to form the insulating paper container having locally different thickness. Description is also found in this literature that the step of printing may include a step of applying an anti-volatility layer in order to form an unexpanded region and a step of laminating high m.p. thermoplastic synthetic resin film on the opposite surface of the base paper.
Japanese Patent Application Disclosure Gazette No. 1997-95368 describes, in regard to the insulating paper container generally comprising the container body and the bottom wall, the process comprising steps of laminating low m.p. thermoplastic synthetic resin film on outer wall surface of the base paper for the container body applying desired region or regions on the upper surface of said film with synthetic resin ingredient containing coating and heating this so as to form expansion-inhibited region or regions corresponding to said region or regions on the outer surface of the container body applied with said synthetic resin ingredient containing coating.
Japanese Patent Application Disclosure Gazette No. 1997-142435 describes, in regard to the insulating paper container generally comprising the container body and the bottom wall, the process comprising steps of providing the outer wall surface of the base paper for the region or regions with printed layer, coating said printed region or regions with a layer of transparent varnish, laminating low m.p. thermoplastic synthetic resin film on the upper surface of said layer of transparent varnish and heating this film so as to achieve a uniform expansion and a satisfactory insulating property.
For every insulating paper container as disclosed in the above-identified documents, it is obviously essential to print various indications on the container body and particularly important to print the point-of-sale (POS) bar codes thereon so that they may be reliably read. In the case of such container having an expanded layer on the printed POS bar codes, said expanded layer often makes it to read the POS bar codes.
Especially for the case in which the POS bar codes are directly printed on the thermoplastic synthetic resin film laminated on the container body followed by expanding treatment, there is an apprehension that the printed bar codes might be deformed or distorted due to expansion of the film and reading of said POS might be adversely affected.
To solve this problem, Japanese Patent Application Disclosure Gazette No. 1995-232774 describes the countermeasure such that the outer wall surface of the base paper for the container body is formed with the expansile layer for printing and at the same time partially formed with the unexpanded region by coating said outer wall surface with the anti-volatility layer. Japanese Patent Application Disclosure Gazette No. 1997-95368 describes the countermeasure such that the upper surface of the low m.p. thermoplastic synthetic resin film laminated on the outer wall surface of the base paper for the container body is partially coated with the layer containing the expansion inhibiting synthetic resin followed by heating treatment in order to form an expansion inhibited region on the outer wall surface of the container body on which the POS bar codes may be distinctly printed. However, both the unexpanded region and the expansion inhibited region inevitably cause the corresponding recess to be formed on the outer surface of the container body which should be smooth Such recess is undesirable from the viewpoint of the convenience for handling as well as of the aesthetic appearance. In addition, the insulating effect sufficient to ensure that the consumer can hold the container without any apprehension of getting burned on the hand cannot be expected in such unexpanded region and expansion inhibited region. Furthermore, the above-mentioned countermeasures of prior art result in unevenness of the insulating property.